ICML CERTIFICATION SERIES
Most of today’s industrial oils use either a mineral or synthetic base oil. These base oils are categorized into five groups according to their refining or manufacturing process. Groups I, II and III represent conventional mineral-based lubricants, while groups IV and V are reserved for manmade synthetic base oils. (Refer to Table I.)
■ Group IV base oils are reserved for Polyalphaolephin
■ Group I reflects what is known as “conventional” base
Specifics of synthetics Synthetic lubricants owe their inception to the early jet engine: They were developed to cope with the extreme temperatures encountered when operating a jet aircraft. Using a polymerization process similar to that used in the plastic manufacturing industry, synthetic base oils are designed with specific and consistent molecular structures that result in highly stable base oils with a very high Viscosity Index (VI) rating. Synthetic lubricants offer many advantages over mineral-based oils, the largest being the ability to operate reliably in both extremes of heat and cold at temperature ranges much wider than mineral oils. In addition to increased VI levels and improved thermal stability, synthetics also demonstrate improved oxidation stability (major reduction of sludge and acid buildup) and lower volatility, resulting in extended lubricant life and reduced oil consumption. The disadvantages of synthetics are primarily associated with their cost—which, depending on the type, can range from as little as three times the cost of a mineral base oil to exponentially more. Certain synthetics can also cause seal swelling, and many are not compatible with any other base oil type. Manufactured from chemically modified petroleum constituents or from a number of chemical bases and compounds, there are five common types of synthetic base oils. Their characteristics and costs compared to mineralbased products are summed up in Table II:
oils. They're made from solvent refined crude stock and have a Viscosity Index between 80 and 120. Their sulfur content is above 0.03%, and their saturated hydrocarbon levels are less than 90%. ■ Group II base oils are refined using a hydro-processing
method known as “hydrotreating” that adds hydrogen to the base oil at temperatures above 600 F. This is done using a catalyst and applying moderate pressure over 500 psi to convert the base stock and reduce its sulfur content to less than 0.03% and increase its hydrocarbon saturation to levels of 90% and above. ■ Group III base oils are known as “bright stock.” They're
primarily manufactured through a severe hydro-processing conversion method known as “hydrocracking" that employs a catalyst at a temperature above 650 F combined with pressures exceeding 1000 psi to take out undesirable elements like sulfur and nitrogen and replace them with hydrogen. The result is a more stable base oil with a Viscosity Index above 120 and a low pour point. In addition, remaining wax compounds are often removed to reduce the pour point further. Due to this more complex refining process, Group III base oils perform in a similar manner to Group IV pure synthetic base oils—and in most countries around the world, including North America, are allowed to be classified as a synthetic lubricant (even though they are hydrocarbon-based).
(PAO) synthetically manufactured base oils made up of very small synthesized hydrocarbon molecules. ■ Group V base oils represent all other synthetic base oil
configurations.
Table I. Base Oil Groups
Group
VI
% Saturates
% Sulphur
Description
I
80-120
<90
>0.03
Solvent processed
II
80-120
>90
<0.03
Hydro processed
III
>120
>90
<0.03
Severe Hydro processed
IV
>140
-
-
PAO - Polyaphaolephin Synthetic
V
>150
-
-
All other base oils not in I-IV and all other synthetics
SEPTEMBER/OCTOBER 2013
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